If the automatic import left you with more than one entry for the same real-world supplier - a distributor plus each of the brands you buy through them, or a few spellings of one name - you can fold them into one. Tick the duplicates on the Suppliers list and click Merge in the bulk bar, then choose the supplier to keep. Purchase orders, item links, pack recipes and auto-assign rules from the others all move to the one you keep, and the duplicates are hidden - nothing is deleted.
Whichever supplier you keep, any contact detail it is missing - address, email, phone, payment terms, currency, lead time, account number, notes - is filled in from the ones you merge away. The supplier you keep never loses a detail it already had. The dialog lists what each row holds, so if the pre-selected supplier says no details yet, you can pick the one with the address instead, or leave it and let the details come across.
The merged names keep working: each one is added to the surviving supplier's Vendors rule, so products carrying that vendor name still land on the right purchase order - and the automatic import will not re-create the entry you merged away.
Renaming behaves the same way. Rename a supplier that came from a vendor name - say, to the distributor's real name - and the old vendor name is added to their Vendors rule automatically, so their products stay assigned and the old entry does not come back on its own.
Good to know
A supplier connected on Stockroom Network cannot be merged into another - disconnect them first, or pick them as the supplier to keep.
Merged suppliers are hidden, not deleted. If you merged before the details started carrying over, the hidden supplier still has everything - open it from the Hidden tab and copy what you need onto the one you kept.
Choose the supplier to keep before you confirm - the merge cannot be undone, though every purchase order and item stays where you can see it.